The present invention relates generally to an optical disc master recording device which is used to make an optical disc master.
As is conventional, various optical disc master recording devices have been used for creating an optical disc master of a compact disc, laser disc, or the like. These commonly known optical disc master recording devices have been constituted such that information is helically recorded on an optical disc master composed of a glass plate having an abraded surface on which a photoresist layer is formed. This recording operation is performed by rotation controlling the optical disc master so as to rotate at a predetermined rotational speed and by sequential feed controlling laser light gathered with an objective lens in an optical head in the radial direction of the optical disc master.
Coarse and fine adjustments are performed so that a spot position of the laser light is caused to agree with a target spot position. The coarse adjustment is performed by causing the entire optical head to drive in the radial direction of the optical disc master and the fine adjustment is performed by causing the objective lens to drive in the radial direction with an actuator in the optical head. In this case, a center position of the objective lens is made the spot position of the laser light, so that the coarse and fine adjustments described above are performed by detecting the center position of the objective lens and then by causing the optical head and actuator to drive so as to eliminate the amount of space between the center position of the objective lens and the target spot position.
Over the years, in order to significantly improve a recording density of the optical disc, information has to be recorded with extremely small track pitch and bit as compared with conventional techniques. However, there is a limit to form a significantly small light spot only with the objective lens as compared with a current light spot.
Incidentally, a method using a solid immersion lens (hereinafter referred to as SIL) is known as a method for further converging the laser light gathered by an objective lens.
FIG. 1 in accompanying drawings illustrates the condition in which a laser light gathered by an objective lens is further converged by an SIL. The laser light from a light source (not shown) is converged by the objective lens A to be incident on the SIL C which is held in a floating head B. The incident laser light is further converged by the SIL C and exposed on an optical disc master D. Incidentally, the objective lens A and SIL C are configured such that they can be driven independently. The number of aperture of the objective lens A can be substantially increased by the SIL C, resulting in the formation of a minute light spot on the optical disc master.
Since two kinds of lenses are provided in an optical disc master recording device having an optical head with the objective lens and SIL shown in FIG. 1, the center position of the objective lens or SIL does not correspond to the spot position of the laser light, respectively. In other words, the positional relationship between the objective lens and SIL causes the position of the light spot to change. Therefore, the position of the light spot on an optical disc master can not be determined only by detecting the center position of the objective lens, as with the devices having been proposed in the prior art. Accordingly, there was a problem in which the current position of the light spot can not be controlled to approach the target spot position in the conventional method.